There have been developed a number of vacuum pumps which attain a vacuum state inside an enclosure by letting gas molecules collide with and get pumped out by fast moving solid, liquid or gas. One example of such pump is a turbomolecular pump. In order for these pumps to obtain an ultra-high vacuum state, however, these pumps must be provided with a mechanical vacuum pump, e.g., a rotary pump or a roots pump, as a back-up pump, making them structurally complicated.
Furthermore, there have been developed other pump using ion-transport effect, a sputter-ion pump and the like. In the sputter-ion pump, the molecules are ionized by electrons moving in helical path in high magnetic field.
The ions thus generated are accelerated to a cathode made of getter materials like Ti or Ta, and sputter the cathode, forming getter film on an anode. This sputtered getter film then removes gases from the enclosure by binding the gases to the surface. This pump, however, operates only in high vacuum, and needs a roughing pump to start with
Further, there is disclosed a vacuum pump in U.S. Pat. No. 4,641,060, entitled "METHOD AND APPARATUS USING ELECTRON CYCLOTRON HEATED PLASMA FOR VACUUM PUMPING", capable of producing a gas pumping plasma within an evacuated enclosure having a collimating system consisting of baffle plate structures and a magnetic field having a central uniform region connected to a source of neutral gas, a magnetic mirror intermediate region and a terminating divergent region. In this apparatus, a desired vacuum level is attained in an enclosure therein by: evacuating the enclosure to a selected pressure; feeding high frequency microwave energy of a selected power and frequency into the magnetic mirror intermediate region; and establishing the magnetic field at a strength such that an electron cyclotron frequency is made to equal to the frequency of the microwave energy within the intermediate region electrons within the magnetic mirror intermediate region, being heated by the microwave energy, the heated electrons ionizing the neutral gas in the intermediate and central regions for creating and maintaining a pumping plasma. Baffle plate structures are provided between the central and intermediate regions and between the intermediate and terminal regions for permitting unobstructed flow of plasma along the magnetic field lines to the terminal region while restricting inward flow of neutral gas resulting from recombination in the terminal region. The plasma is preferably composed of ionized neutral gas from the central and intermediate regions and an adequate neutral gas concentration is maintained in the intermediate region by controlled supply of make-up gas.
This pump, however, as in the case of turbomolecular pumps, must be equipped with a back-up pump. Further, since it utilizes microwave and a large number of magnets for controlling the plasma flow, it is structurally complicated and expensive to construct.